Technical Field
The present invention concerns a method of operating a wind power installation and a wind power installation.
Description of the Related Art
A wind power installation having a horizontal-axis rotor has at least one and usually three rotor blades which in ordinary operation rotate about a horizontal axis due to the wind incident thereon to generate electric energy by means of that rotary movement. If excessively strong wind is incident on the rotor blades the wind power installation can suffer damage—depending on the frequency or strength. Such loadings due to excessively strong wind can be countered, for example, by the rotor blades being at least partially turned out of the wind. That is also referred to as pitching.
To be able to initiate such measures or other measures for relieving the load on the wind power installation it is necessary to detect corresponding loadings due to strong wind. A continuously strong and uniform wind can be detected by the behavior of the wind power installation such as for example the resulting energy production. For short-term loadings or also for local loadings on for example only one rotor blade, sensors can be provided for measuring such a loading. Thus for example sensors such as strain gauges are used for detecting the flexing of each rotor blade. In that way a loading related to flexing of the rotor blade can be directly detected qualitatively and also quantitatively and correspondingly evaluated in order possibly also to take steps to limit the loading.
A prerequisite in that respect is that the corresponding loading sensors operate precisely and supply reliable values. For that purpose calibration and/or adjustment of the respective sensor is also quite essential. It is usual that sensors such as for example a strain gauge supply a strain-dependent resistance value or—depending on the respective electronic evaluation system connected downstream thereof—a strain-dependent signal such as for example an output signal. Those values are then to be associated with an associated loading on the rotor blade by means of calibration and adjustment.
Such calibration with adjustment can be very complicated and expensive and also liable to error because in that case associated loading values, which are to be recorded elsewhere, are to be associated with the measured sensor values. One possible way of effecting calibration with adjustment is pulling the blade manually with a comparative force which is to be measured so that calibration is effected on the basis of that comparative force. Thus for example a rotor blade in a 6:00 hours position can be pulled at its tip towards the pylon while the force applied is measured.
Added to that is the fact that relationships change in the course of operation of the wind power installation. That can be triggered by aging phenomena both of the rotor blades and also the sensors and also due to other reasons such as for example defects in the sensor or its fixing. If such changes are slight and/or occur slowly there is the danger that they remain unnoticed.
As state of the art attention is directed to DE 10 2006 036 157 A1.